tractability

Tractability is a term used to describe the practical solvability of computational problems or models as their size grows. In computer science and mathematics, an algorithm or problem is considered tractable if it can be solved within resource bounds that scale reasonably with input size, typically meaning polynomial time or other feasible growth rates.

A common yardstick is the class P, which consists of problems solvable in polynomial time by a deterministic algorithm. Problems outside P may be intractable in the worst case, with many known to be NP-hard or undecidable, indicating that efficient (polynomial-time) solutions are unlikely in general. However, tractability can be context-dependent; for some problems, acceptable performance is achievable in practice with good implementations, average-case analysis, or problem-specific heuristics.

Parameterized complexity offers a finer notion of tractability. A problem is fixed-parameter tractable (FPT) if it can be solved in time f(k) · n^O(1), where k is a chosen parameter and f is some computable function. This can yield efficient solutions for small parameter values even when the overall problem is hard.

In optimization and operations research, tractability distinguishes problems that can be solved efficiently from those that are typically hard. Linear programming is considered tractable, while general integer programming is NP-hard, though modern solvers and approximation methods expand practical tractability for many instances.

Tractability also encompasses approximate and heuristic approaches that yield near-optimal or good-enough solutions within reasonable time. Overall, the concept balances theoretical worst-case complexity with empirical performance and resource constraints.